PVC/twine dispenser for pheromones

ABSTRACT

A novel dispenser for the release of insect attractants has been invented for baiting insect traps. The dispenser is comprised of a flexible support coated with a polyvinylchloride (PVC)-insect attractant mixture. A PVC/twine dispenser has been found to be particularly effective for the release of the gypsy moth pheromone, (+)-disparlure.

This is a continuation of application Ser. No. 07/765,732 filed Sep. 26,1991, now U.S. Pat. No. 5,342,618, herein incorporated by reference.

I. BACKGROUND OF THE INVENTION

The gypsy moth, Lymantria dispar L., is a major forest pest in thenortheastern United States, and spot infestations appear elsewhere.Monitoring existing gypsy moth populations and detecting new populationsis achieved by utilizing traps baited with polymeric, controlled-releasedispensers containing the sex attractant pheromone,(7R,8S)-cis-7,8-epoxy-2-methyloctadecane, or (+)-disparlure, whereinmale moths are lured into the traps by the pheromone. When such luresare used in conjunction with insecticides, the moths are killed insidethe traps.

The pheromone, disparlure, was identified, synthesized and reported inthe literature by Bierl et al. (Science, 170:87-89, 1970). The opticalcharacter of the pheromone structure was later determined to be the(+)-enantiomer by Yamada et al. (J. Insect Physiol, 22:755-761, 1976).The pheromone has since been used in traps for the detection of gypsymoth populations and is commercially available. Its relatively highcost, however, dictates that the dispenser utilized must deliver nearlyall of its pheromone content over one entire flight season of the moth.Otherwise, residual pheromone in the dispenser at the end of the seasonis wasted when the dispenser is discarded. It is equally important thatthe supply of the pheromone not be depleted before the end of the flightseason.

In these types of traps, therefore, one must regulate the amount ofpheromone released from the dispenser in the trap so that there is abalance between a rate of release sufficient to lure the moth into thetrap and the length of time that the trap must remain attractive (oneflight period). The dispenser must not deliver the pheromone so rapidlythat the trap does not provide adequate luring capabilities over theentire flight period of the moth.

The pheromone (+)-disparlure is sufficiently volatile that the compoundmust be formulated in a controlled-release dispenser in order to prolongits evaporation and thus extend the duration of its effectiveness. Sincethe early 1980's, a dose of approximately 500 mg of (+)-disparlure in aplastic laminate dispenser (Hercon Environmental Co., Emigsville, Pa.)has been used to bait a standard milk-carton gypsy moth trap used in allFederal and State detection programs (Schwalbe, C. P. in Technical Bull.1584, USDA, Washington, D.C., pp. 542-549, 1981, Doane and McManus,ed.).

Normally, in assembling such traps, a twist tie is suspended within thetrap by stapling it to the apex of the trap. The conventional pheromonedispenser is attached to the twist tie while an insecticide-impregnatedstrip is similarly attached near the dispenser. This is a laborintensive and tedious process since approximately 300,000 traps arerequired nationally each year.

Other commercial dispenser systems have been evaluated, but none hasproven as effective as the plastic laminate device. Other commercialdesigns have included rubber septa, polyethylene tubes, silicone rubber,semi-permeable membranes over a reservoir and thermoset matrices.

A polyvinylchloride (PVC) pellet has also been tested which containseither 1250 or 2500 mg of (+)-disparlure. Even at these relatively highdoses, the release rates are initially low, i.e. only 57 and 97 ng/hr,respectively, as compared to the release rate (ca. 130 ng/hr) given offby the standard laminate containing only 500 mg of pheromone. The lowrelease rates per quantity of pheromone in the PVC pellets result from alow pheromone to polymer ratio and from a low surface area (ca. 75mm²)for evaporation of the (+)-disparlure. After 16 weeks of greenhouseaging, which is equivalent to at least two flight seasons, these PVCpellets still contain at least 75% of their initial dose of pheromone.Thus, most of the pheromone is wasted in this type of dispenser sincethe planned use is for only one season.

PVC was used as a matrix for dispensing an insect pheromone byFitzgerald et al. (Environ. Entomol., 2:609-610, 1973) when highquantities (1-20% by weight) of the cabbage looper pheromone wereincorporated in 70-mm long PVC cylinders. Since then, other pheromoneswere formulated in PVC forms, including the pheromone of the tobaccobudworm, the boll weevil and the spruce budworm. The forms of thepreviously described PVC dispensers were a solid mass such as a slab,disc, rod, etc. which had a limited surface area for evaporation andrelease (See Weatherson, I. in Insect Pheromones in Plant Protection,Jutsum and Gordon, eds., John Wiley & Sons, New York, pp. 249-280, 1989,a review article).

The dose of pheromone per dispenser was substantially higher(2000-10,000 mg or more) in previously reported PVC applications thanthat used for the laminate dispenser (500 mg). Only PVC pellets designedfor monitoring spruce budworm contained a relatively low dose (0.03% byweight), but those dispensers were shown to be unsatisfactory in fieldperformance. The volatility of pheromones incorporated in previous PVCapplications was higher and their cost substantially lower than that of(+)-disparlure, thus obviating a need to develop a PVC dispenser havingan increased surface area for increasing its release rate or having anoptimal efficiency for delivering its total pheromone content over aparticular period of time. Thus, the need exists for a dispenser whichwill give a sufficient pheromone release rate while at the same timeprolonging the rate of release such that pheromone is released over theentire insect flight period in a given area and delivers essentially allof the pheromone contained within the dispenser over that period.

II. SUMMARY OF THE INVENTION

We have now discovered that a dispenser which meets the aboverequirements can be made by coating a support with a mixture of aninsect attractant and PVC, where the attractant is present in themixture in an amount sufficient to lure an insect for which it iseffective. Accordingly, it is an object of the invention to provide anovel dispenser which will provide a lure release rate sufficient toattract an insect for a time period which covers the entire flightseason of the target insect. To meet this objective, a dispenser havinga high surface area and coated with a thin film of the PVC-attractantmixture is provided, thereby permitting the dispenser to releaseattractant at an effectively high rate while at the same time prolongingits delivery over the entire flight season.

It is a further object of the invention to provide a trap comprising thenovel dispenser in combination with a housing for the attachment of thedispenser. One embodiment of the trap optionally includes an insecticidein an amount sufficient to kill a trapped insect.

Another object of the invention is to provide a method of making thenovel dispenser.

It is also an object of the invention to provide a method of using thenovel dispenser for luring targeted insects of interest.

Other objects and advantages of this invention will become readilyapparent from the following description.

III. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph of aging data of (+)-disparlure as a function of thelength of greenhouse aging.

FIG. 2 is a graph of (+)-disparlure release rates as a function of thelength of greenhouse aging.

FIG. 3 is a graph of comparison data of (+)-disparlure release ratesfrom oven-aged dispensers.

IV. DETAILED DESCRIPTION OF THE INVENTION

The primary novel feature of the instant invention is a flexible supportthat has been coated with a mixture of PVC and an insect attractant. Asuitable flexible support includes any multi-stranded material such astwine, string, thread or cord that is weatherable for the duration ofits use. Such supports may be cotton, nylon or the like, or blends ofsuch materials, and they are usually twisted, braided or woven to givethe material strength. The preferred support for this invention is aloose twisted twine, in particular nylon twine. Especially preferred istwisted nylon twine having a break strength of about 150 to 200 lbs.,preferably about 165 lbs.

The flexible support is coated with a mixture of a curable PVC polymerand the insect attractant of interest. The particular PVC used can beobtained commercially and is not critical so long as it is convenientlycurable by conventional methods either at room temperature or elevatedtemperatures, and with or without catalysts present. Suitable curableliquid PVCs may be obtained from Sinclair & Rush, St. Louis, Mo. andhave the designation No. 516-89. Such PVCs are curable at elevatedtemperatures (up to about 200° C.) in an oven over short periods of time(about 1 minute to about 30 minutes).

Insect attractants are commercially available. They are blended with thecurable PVC prior to coating the flexible support. The coating processglues the individual strands together to form one composite strand.After coating, the support should contain 10 to 100 mg/cm of the insectattractant, depending upon the volatility of the particular attractantused. The support can then be cut into pieces of a size to give thedesired quantity of attractant. The high ratio of surface area per mg ofPVC-insect attractant mixture in the dispenser enhances the rate ofevaporation of the attractant and efficiently delivers most of theactive compound over the duration of the flight period. Thus, theresulting product is a novel dispenser of a flexible material containingan insect attractant in a thin, cured PVC coating. As will be shown bythe examples presented herein, this dispenser gives the optimumdesirable release rate.

The novel dispenser of the instant invention contemplates the use of abroad range of insect attractants. A critical factor in the selection ofa useful attractant is the volatility of the compound: the attractantmust be sufficiently volatile when blended with PVC that it willmaintain an effective release rate over a selected time period.Attractants of particular interest for use herein are pheromones of thecabbage looper, the tobacco budworm, the boll weevil, the spruce budwormand other insects for which a pheromone is known. Of particular interestis the use of the pheromone of the gypsy moth, (+)-disparlure.

The novel dispenser of the instant invention is prepared by initiallycoating the flexible support material with the PVC-attractant mixture byany conventional means such as dipping the support in the mixture orbrushing the mixture onto the support. A particularly effective coatingmethod involves threading the flexible material through a syringe barreland out an orifice drilled in a Luer cap, leaving the remainder hangingout of the top of the barrel. Prepared PVC-attractant mixture is pouredinto the syringe barrel, and the support is pulled through the orifice.This procedure results in a thin, uniform coating on the support whichgives the optimal release rate of the attractant. Following the coatingprocedure, the coated support is loosely coiled and laid on a glassplate in an oven to cure. The cured product is then cut into desiredlengths for attachment to the particular trap configurations selected.

The novel trap of the instant invention may be effectively utilized inmethods for monitoring known insect infestations or detecting new ones.Traps are placed in positions appropriate for the insect of interest fora period of time sufficient for the attractant to effectively lureinsects into the trap. For example, when monitoring or detecting gypsymoth infestation, one deploys traps according to the instant invention,wherein the attractant is (+)-disparlure, in wooded areas suspected ofhaving infestation over the entire flight period of the moth, usuallyfrom four to six weeks. For optimum results, the traps should be inplace about one month before the flight period begins.

The novel invention is applicable in any instances wherein the insectattractant has sufficient volatility to provide an effective releaserate. The experimentation required to determine such volatility would beconsidered of a routine nature and well within the level of skill in theart.

The following examples are intended only to further illustrate theinvention and are not intended to limit the scope of the invention asdefined by the claims.

The trap of the instant invention comprises the novel dispenserdescribed supra and any conventional commercial trap which normallyutilizes a dispenser suspended from, or attached to, the interior of thetop of the trap. A milk carton type trap wherein the dispenser isfastened to the top interior apex of the carton is an example of such atrap. As discussed supra, conventional traps for the gypsy moth are madeby fastening a twist tie to the interior apex of the trap, followed byattaching a dispenser to the twist tie, resulting in a two-stepmanufacturing method. An ancillary advantage of the novel dispenser isthat it may be stapled directly to the apex of a trap thus eliminatingthe step of fastening a twist tie or other such attachment device to thetrap. Optionally, an insecticide effective for the insect of interestmay be additionally contained within the trap in a configuration whichis suitable for acting on the particular target insect.

V. EXAMPLES

Laboratory and field tests have been designed to measure the efficacy ofpheromone dispensers for gypsy moth detection. The measured parametersinclude: initial dose of pheromone, rate at which the pheromone isreleased, number of male moths captured per trap, and effect of durationof exposure on these quantities. The quantity of (+)-disparlure in adispenser, either initially or after exposure, is measured by gaschromatography on a solvent extract of the dispenser using a knownsolution of (+)-disparlure as an external standard. The rate of releaseof (+)-disparlure from the dispenser is determined by trappingvolatilized pheromone over a 6-hr period from a dispenser housed in aglass chamber within an oven set at 35° C. A constant air flow of 100ml/min through the chamber transports the pheromone to the trap, and thequantity of trapped pheromone is then determined chromatographically.

Example I Method of Making Dispensers

Liquid PVC, No. 516-89, was purchased from Sinclair & Rush, St. Louis,Mo. 63111. Twisted nylon twine, break strength 165 lb, no. 18, item no.00089 was purchased from Duraline Products, Crowe Rope Co.,Warren, Me.04864. Neat (+)-disparlure, density=0.87 g/ml, was supplied and approvedby USDA-APHIS.

The appropriate volume of (+)-disparlure was syringed into and blendedwith a known weight of the liquid PVC to give a concentration of 6.9 mlof attractant per gram of liquid PVC (or 0.6% by weight). Blending wascarried out using a VirTis, homogenizer (VirTis Co., Inc., Gardiner,N.Y., model 45 or alternate) run at about ⅓ maximum speed for 1 minute.The end of a length (ca. 100 cm) of twine was threaded through a 5-mlglass syringe barrel with a Luer lok, fitting and out the orifice of afemale Luer cap through which a 1.37 mm hole had been drilled. The endof the twine was coated with glue and shaped to a point to facilitateits insertion through the orifice. The PVC-(+)-disparlure mixture waspoured into the syringe barrel, and the twine was pulled through theLuer cap orifice at a rate of approximately 30 cm/min. Additionalmixture was added to the barrel as needed. The coated twine was looselycoiled and laid on a glass plate in a 170° C. oven for 3-5 min to cure.The resulting (+)-disparlure concentration in the coated twine wasapproximately 30 mg/cm. Lengths of 16.7 cm containing ca. 500 mg ofattractant were cut for affixing to traps.

Example II Greenhouse Aging

Since the gypsy moth flight is of relatively short duration, the effectof exposure on the dispensers and their measurable parameters wasassessed by placing dispensers in a greenhouse set at 32-38° C. forperiods of time ranging from 2 to 16 weeks prior to gypsy moth flight.These pre-aged dispensers were then compared with unaged dispensers inlaboratory and field tests. The effect of greenhouse exposure onpheromone content and release rate and on moth capture can thus bedetermined and is shown in Table 1. Since greenhouse temperatures arehigher than those generally found in field situations, dispenser agingis accelerated in the greenhouse. A dispenser which can remainattractive after 16 weeks in a greenhouse has been shown to remainhighly attractive throughout a flight period. In the case of theconventional laminate dispenser, for example, a residual content of atleast 100 mg of (+)-disparlure and a release rate of 30 ng/hr assureshigh insect capture. FIGS. 1 and 2 graphically show comparative databetween conventional laminate dispensers and the novel PVC/twinedispenser of the instant invention with respect to pheromone content andrelease rate as a function of greenhouse aging. It can thus be seen thatthe novel dispenser compares favorably with the conventional dispenserin these two respects.

TABLE 1 Residual (+)-disparlure contents and release rates of laminateand PVC/twine dispensers after 0, 4, 8, 12, and 16 weeks of greenhouseaging. Content (μg) at Week Release rate (ng/h) at Week Dispenser 0 4 812 16 0 4 8 12 16 laminate-1988 452 268 145 104 114 130.5 112.6 78.765.0 47.1 laminate-1989 520 167 111 86 23 131.5 99.0 43.3 29.0 24.6PVC/twine 461 316 237 139 97 111.5 89.8 61.2 45.9 31.6

Example III Field Tests

Field tests were conducted to compare the PVC/twine dispenser with twolots of conventional laminate dispensers (1988 and 1989 lots).Greenhouse aging periods for each dispenser were 0, 4, 8, 12 and 16weeks. Five replicates of each treatment were tested. Effectiveness wasdetermined by numbers of male moths captured (n), which, for analyticalpurposes was transformed to (n+0.5)^(½). Results are shown in Tables 1and 2.

TABLE 2 Mean numbers of males¹ captured per trap in each of threeobservations in Test 1, 7/18-7/23, 1989. Weeks of Greenhouse AgingDispenser 0 4 8 12 16 laminate-1988 87.8 a 105.6 abc 144.6 ab 128.5 a 80.5 ab laminate-1989 74.4 a 114.1 ab 157.2 a 144.7 ab  58.5 cPVC/twine 43.9 bc 111.9 ab 135.3 abc 110.0 abc 100.4 a ¹Within a column,means followed by the same letter are not significantly different at the5% level of significance according to the Duncan's Multiple Range Test.

Based on the field test results, batch-to-batch variation in laminatedispensers is apparent since the 1988 laminate remained attractivelonger than the 1989 laminate. This variation has been observedfrequently in the past and, in part, motivated the search for analternate dispenser. The PVC/twine dispenser gave higher moth capturesthan either laminate after 16 weeks of aging and, with the possibleexception of the 0-time period, gave moth captures that were notsignificantly different from those with the better (1988) laminate . Inaddition, Test 2 included a cotton wick freshly treated with 100 mg of(+)-disparlure, the standard adopted by APHIS for assessing efficacy ofall dispensers, and the results show that the moth capture of thePVC/twine dispenser at all aging periods was not significantly differentfrom the standard.

TABLE 3 Mean numbers of males¹ captured per trap in each of fourobservations in Test 2, 7/23-7/27, 1989. Weeks of Greenhouse AgingDispenser 0 4 8 12 16 laminate- 175.1 a 159.6 abc 124.0 a-d 130.3 a-d 97.5 cd 1988 laminate- 161.0 ab 145.1 abc 102.4 b-d  95.5 b-d  58.7 e1989 PVC/twine 111.2 a-d 130.6 a-d 124.7 a-d  83.4 d 135.1 a-d Cotton154.1 ab 100 μg ¹Means throughout the table followed by the same letterare not significantly different at the 5% level of significanceaccording to the Duncan's Multiple Range Test.

Example IV Laboratory Test

A laboratory test was conducted to compare the release rates of thePVC/twine dispenser and the 1989 laminate dispenser as a function ofduration of exposure in a laboratory oven at 59° C. under constant airflow of 100 ml/min. These conditions were used to accelerate the loss ofpheromone. The release rates were measured periodically at 35° C., andthe results are shown in FIG. 3. At the conclusion of the test (370 hrat 59° C.), the laminate dispensers contained an average of 0.09 mg andthe PVC/twine dispensers an average of 118 mg of (+)-disparlure perdispenser. These data parallel those obtained on greenhouse-ageddispensers and again show that the PVC/twine dispenser slows the releaseof a nominal 500 mg dose of (+)-disparlure as compared to theconventional laminate dispenser. As a result, the duration of efficacyof the PVC/twine dispenser is longer than that of the laminate.

As shown by the Examples, a PVC-coated flexible dispenser has beeninvented which prolongs the duration of high attraction. Because of thisdispenser's effectiveness, baited traps can be deployed in the fieldwell in advance of insect flight. In addition, the dispenser can alsoreplace both the twist tie and the laminate dispenser currently used toprepare traps.

It is understood that the foregoing detailed description is given merelyby way of illustration and that modification and variations may be madetherein without departing from the spirit and scope of the invention.

We claim:
 1. A dispenser comprising a flexible support of multi-strandedmaterial, having coated thereon a mixture of PVC and an insectattractant in an amount sufficient to lure an insect for which saidattractant is effective.
 2. The dispenser of claim 1, wherein the insectattractant is a pheromone.
 3. An insect trap comprising a housing andthe dispenser of claim 1 attached to the inside of said housing.
 4. Thedispenser of claim 1, wherein said flexible support is selected from thegroup consisting of twine, string, thread, and cord.
 5. The insect trapof claim 3, wherein the insect attractant is a pheromone.
 6. The insecttrap of claim 5, wherein said trap additionally comprises an insecticidein an amount sufficient to kill an insect trapped within said housing.7. A method of luring insects, wherein the trap of claim 3 is placed ona support in an area suspected of being infested with said insects, fora period of time sufficient to permit the attractant to effectively lureinsects into the trap.
 8. The method of claim 7, wherein the attractantis a pheromone.
 9. The method of claim 8, wherein said trap additionallycomprises an insecticide in an amount sufficient to kill an insecttrapped within said housing.
 10. The method of claim 9, wherein theperiod of time is one flight period.